Vet´s Perspective

Jul 13, 2012
by WLJ
Heat management

As the past few weeks have demonstrated, heat can really take its toll on us as well as our livestock. According to previous physiological studies, ambient temperatures at only 75 to 80 degrees Fahrenheit are capable of inducing heat stress in cattle. Now think about the additional stress during the recent 110-degree episodes we have been experiencing!

Cattle under heat stress initially are not at severe risk, but must be replenished appropriately in order to maintain a normal biologic balance. Fermentation in the hindgut adds more heat to the animal as well. For the most part, cattle cannot dissipate heat, or sweat, as effectively as many other animals and therefore rely on respiration as a major cooling aid during warmer weather conditions. A lack of adequate cooling during evening hours may perpetuate the problem, as animals are unable to fully restore a normal temperature balance.

One study reported that cattle may take up to six hours to dissipate heat after peak environmental temperatures.

Signs of heat stress may appear vague but are common with high heat episodes, such as: decreased feed intake, restlessness, increased salivation, or heavy and rapid respiration. A severe sign is that of open mouthed breathing with labored effort.

Animals most at risk for heat stress are those with dark colored coats, heavy body condition scores, and those suffering respiratory compromise due to conditions such as pneumonia.

Large amounts of fat deposits ultimately prevent cattle from proper heat regulation. Animals with respiratory disease are also limited in their cooling abilities via inadequate respiration.

One of the main ways to avoid heat stress is to work cattle during the early morning hours. The body temperature continues to rise via accumulated heat as the day goes on, so cattle being worked even in late afternoon may still suffer from heat exhaustion. Maintain shorter processing lines in order to prevent long wait times during full sunlight hours.

The water requirements of any animal will greatly increase during high ambient temperatures. Cattle suffer water loss due to increase in respiration and perspiration. Additional water tanks should be made available and kept clean in order to enhance consumption. Cattle will drink upwards of 1 percent of their body weight per hour; thus, a 1,000-pound animal should be offered approximately 1.5 gallons of water per hour.

Fermentation from feed intake also increases between four and six hours after feeding. This may cause cattle that are fed in the morning to have higher body heat from fermentation during the noon hour temperatures. It may be wise to portion out a greater percentage of feed four hours after the peak ambient temperature.

General recommendations for effective shade are for each animal to have between 20 to 40 square feet of relief from direct sunlight. Shade structures should be about eight feet in height in order to allow adequate air movement.

Cattle often huddle together more as a repelling aid from biting flies and midges. Routine use of insecticides can decrease fly populations immensely, and thus allow animals to spread out more over a given area and enhance air movement throughout a pen.

Cooling devices such as sprinklers have shown to be a great aid during heat stress. A sprinkler system can increase the evaporative cooling ability as well as decrease ground temperature.

It is important that cattle are accustomed to the water spray—plan to use a sprinkler system before intense heat so that animals do not shy away from being misted. Prior exposure to sprinklers is also important in preventing cold shock to animals.

Producers can manage their herds by keeping watch of the temperature humidity index (THI). If THI is over 80, cattle are likely to have heat stress signs. USDA has a forecast of THI levels; one may be directed to this link for further information: http:// docs.htm?docid=20426. — Dr. Genevieve Grammer

[Dr. Genevieve JM Grammer is a veterinarian working out of the Pikes Peak region. Please address correspondence to]